He suffered a fatal heart attack 43 minutes after he was administered the first in what was to be a lethal three-round drug cocktail. Three minutes after the injection of midazolam, Lockett seized and writhed in pain. He was unconscious ten minutes after the drug was administered, dying roughly a half hour later.

Obama said at a joint press conference with German Chancellor Angela Merkel at the White House that what happened was “deeply troubling,” though he added that the application of the death penalty “may be appropriate” for Lockett’s “heinous, terrible crimes.”

Lockett, a four-time felon, was convicted in 2000 for the 1999 shooting of 19-year-old Stephanie Neiman and watching as accomplices buried her alive. Neiman interrupted Locket and his accomplices, who are both serving life sentences, as they attempted to rob a private residence.

Still, the U.S. President noted “significant problems” the U.S. has in the application of the death penalty, including racial bias, what he termed as an uneven application of the death penalty and some situations where an individual on death row was later discovered to be innocent.

The White House first struck out against the botched execution on Wednesday, saying that it did not live up to humane standards.

“We have a fundamental standard in this country that even when the death penalty is justified, it must be carried out humanely,” said Jay Carney, the White House Press Secretary while speaking to the press.